Method of water purification

ABSTRACT

The invention provides a method for the removal of biological species, such as  Cryptosporidium , from water using aluminum based media which contains surface Al—OH groups.

TECHNICAL FIELD

The present invention relates to a method for the purification of water.More particularly, the present invention relates to the removal ofmicrobiological contaminants from water.

BACKGROUND ART

The presence of microbial pathogens in water bodies, such as rivers,dams, seawater and swimming pools, where human contact is likely tooccur, or, in water intended for human or animal contact and/orconsumption, is a potential hazard with the potential to result inillness, disability or even death where these pathogens areinadvertently ingested by humans or animals, Accordingly, there exists avariety of methods for their removal so as to render contaminated watersafe for human contact and/or consumption.

Known methods of removing pathogens from contaminated water includemechanical filtration, i.e. physical exclusion based on the size of themicrobial pollutants, chemical treatment such as chlorination andozonation and electrolysis which generates oxidants fatal to thepathogens.

Cryptosporidium can survive up to six months in a moist environment andhave been known to contaminate public swimming pools. Several outbreaksof cryptosporidiosis due to contaminated swimming pools have beenreported. the contamination is usually due to faecal accidents in thepool and the spread of infection amongst pool users can be rapid. Thisis partly due to the ineffectiveness of current disinfection procedures.As swimming pools do not normally monitor for Cryptosporidium, awarenessof a problem is invariably through incriminating epidemiologicalevidence. In many cases, cryptosporidiosis manifests as infectiousdiarrhoea with risks of complication in theimmunocompromised/immunosuppressed population, for example the veryyoung, the very old, transplant recipients and those undergoingimmunotherapy.

In the case of raw water, Cryptosporidium oocysts may be removed byconventional water treatment processes during the production of potablewater. These processes involve coagulation with coagulants such asferric chloride or alum followed by addition of polyelectrolytes ascoagulant aids and in some cases high molecular weight polymeric organicfilter aids. The coagulated material is removed by either sedimentationor filtration through sand filters.

Water treatment processes are not completely reliable for the removal ofCryptosporidium oocysts and in many cases oocysts breakthrough the plantinto the reticulation system. Accordingly conventional disinfectants,such as chlorine or ozone, are added to the filtered water prior toreticulation as a precaution in order to destroy some common water bornepathogenic microorganisms that may have broken through the watertreatment plant. However, Cryptosporidium oocysts are unaffected bythese disinfectants.

In addition, it is always possible that viable microorganisms may beintroduced between the water treatment plant and the domestic user. Thismay occur by sewage infiltration.

Therefore Cryptosporidium oocysts that enter into the reticulationsystem pose extremely serious public health concerns since no cureexists for cryptosporidiosis.

In addition to potable water, water in swimming pools, spa pools andother recreational waters may contain, Cryptosporidium mainly throughfaecal contamination introduced by pool users as well as potentiallythrough the potable water used in the swimming pools.

Normally in swimming pools and spas, the water is continuously filteredthrough sand filters to remove particulate material and disinfected bychlorine addition followed by recirculation. In some instances lowconcentrations of inorganic coagulants are added to optimise solidsremoval. However, if Cryptosporidium contamination occurs, removal byfiltration or coagulation/filtration through sand filters may not becompletely effective. Detection of oocysts results in pool closure forthe treatment of the water, for example, by superchlorination at a levelof 3-5 mg/L. The efficiency of superchlorination as treatment fordeactivating Cryptosporidium is not guaranteed. The use of otherstronger disinfectants such as ozone, chlorine oxide or mixtures ofstrong oxidants has also been tested with mixed success.

Thus whilst there are a number of processes well recognised for thetreatment of water sources to produce potable water or to treatrecreational waters, a significant problem remains in the ability ofthose processes to produce water, particularly potable water, thatcomplies with strict regulatory requirements in relation to pathogenicmicroorganism content. Regrettably, conventional water treatmentprocesses have proven unreliable for their removal from water sources.

The present inventors have recognised the critical importance ofproviding a means by which microorganisms, particularly pathogenicmicroorganisms, that may remain after conventional water treatmentprocesses may be removed prior to the distribution of the potable waterto the end users.

DISCLOSURE OF INVENTION

The present inventors have now discovered that aluminium based mediapossessing surface Al—OH groups provides a means for the removal ofpathogens present in water.

Accordingly, in a first aspect the present invention provides a methodfor the removal of biological species from water comprising the step ofcontacting the water with an aluminium based medium which containssurface Al—OH groups for a time and under conditions such that aproportion of the biological species are adsorbed onto said medium andremoved from the water.

In a second aspect, the invention contemplates the use of an aluminiumbased medium which contains surface Al—OH groups in the removal ofbiological species from water.

The present inventors believe that for the first time, this inventionprovides a practical way to remove dangerous water borne pathogens, suchas Cryptosporidium, using a process which is readily adaptable toexisting water treatment processes.

Many pathogens possess active surface groups, such as carboxylate andphosphate groups associated with cellular glycoproteins, which areavailable for interaction, for example, by chemical or electrostaticmeans, when contacted with active surface groups of an external medium.One particular pathogen is Cryptosporidium, which the present inventorshave found possesses a pk_(a) value of 2.5 suggesting the presence ofnegatively charged groups (such as carboxylate or phosphate groups) onthe organism's surface. Additional studies indicated that maximumnegative surface potential of around −27 mV was achieved at a pH greaterthan 5.7 in aqueous solution.

Close contact between surfaces can result in the formation of chemicalbonds between surface sites on the approaching surfaces. This is calledchemisorption and typically occurs between carboxylate, phosphate andwide range of metal cations such as aluminium, calcium, iron etc. innatural systems. The precise nature of these chemical interactions isoften complex but may involve ligand bonding to carboxylate andphosphate groups on the surface of micro-organisms. In addition, van derWaals forces generally act to pull colloids together into strongadhesive contact.

Thus, as used herein, the terms “adsorb” and “adsorption” may refer toeither electrostatic adsorption or chemisorption.

The biological species for removal by the method of the inventioninclude human or animal pathogens such as protozoa exemplified byCryptosporidium and Giardia, bacteria exemplified by Pseudomonas,Escherichia coli, and Vibria cholerae, viruses, exemplified bypoliovirus 1 and coliphage MS-2 and algae.

A preferred aluminium based medium for use in the invention is alumina(Al₂O₃) which is hydrated at the surface so as to form surface Al—OHgroups. This material presents a chemically active substrate for thedirect adsorption of suitable biological species. Surprisingly, thepresent inventors have found that surface hydrated alumina has theability to strongly bind microorganisms especially protozoa such asCryptosporidium and Giardia. It is, however, critically important thatthe alumina is in the appropriately hydrated form.

The alumina may be presented in any number of physical forms such aspowders, granules, crystalline solids, or compressed discs or wafers andmay exist in the amorphous state or as α-Al₂O₃ or γ-Al₂O₃.

Particulate alumina, such as powdered and granulated forms, provide anincreased surface area per volume and are suitable for packaging intocartridges which can be used alone or in conjunction with otherfiltration systems. Powdered and granular alumina is readily availablein different diameter size ranges for example, from about 15 mm down toabout 50 microns (0.05 mm). The size of the particulate alumina used maybe varied depending on the application. By way of example only, oneparticulate size range contemplated by the invention is from about 5 mmto about 1 mm for example, about 3-2 mm. Another particulate size rangeis from about 1.5 mm to about 0.5 mm. Yet another particulate size rangecontemplated by the present invention is from about 0.5 mm to about 0.05mm, for example 0.3 mm to about 0.1 mm.

Depending on the application generally the particle sizes will bebetween 500 microns (0.5 mm) to 13 mm. The most suitable size range willbe selected in terms of effective size and uniformity coefficient.

In the case of municipal water treatment, usually larger particles size,typically greater than 1 mm would be preferred in order to achieveappropriate water throughputs. However, pilot plant testing may becarried out to establish the optimum relationship between the thicknessof the alumina bed and the particle size to ensure maximum removalwhilst maintaining high water throughputs.

Similarly in the case of water treatment for industrial purposes, suchas in the preparation of water for use in the manufacture of food andpharmaceuticals, relatively large volumes of water will be treated.Accordingly, a similar approach to municipal water will usually beadopted. It must however, be realised that the use of filter cartridgescontaining the hydrated alumina may be desirable in some manufacturingfacilities.

In both municipal and private swimming pools applications it may beappropriate to use finer particles, say between 0.5-2 mm to maximisecollision and capture of biological species by the particles.

In the purification of domestic water it would be appropriate to usesmallest particle sizes to both minimise the size of the filter deviceand to achieve maximum surface area whilst ensuring that pressure dropsacross the filter cartridge containing the alumina are minimised.

It is within the scope of this invention to utilise the hydrated aluminaas part of a mixed filter bed. In this form, the hydrated alumina isgenerally disposed on the downstream side of the inflowing water. Inthis way, the water will preferably have been conventionally treatedprior to contacting the hydrated alumina. The person skilled in the artwill appreciate that the mixed filter bed may include discrete beds ofhydrated alumina of different particle size ranges.

It is also important to appreciate that in some applications, it may bepermissible to utilise beds of hydrated alumina that are fed undergravity.

In order to maximise the adsorptive capacity of the hydrated alumina forbiological species, preferably the alumina bed will be used as polishingfilter. Thus, in some embodiments of the present invention it isenvisaged that the hydrated alumina will be used as a separate polishing“monofilter” after the conventional filters that remove the flocs fromthe flocculated raw water, In this configuration it is easier to takethe filter off-line when it is exhausted in order to chemicallyregenerate the alumina. It must be recognised that there may be someapplications where the alumina may be used with little or nopretreatment of the inflowing water.

Prior to contacting the water with the hydrated alumina, in the case ofthe treatment of municipal water, both turbidity and colour are usuallyremoved by the addition of suitable inorganic coagulants and organicpolyelectrolytes. If the municipal water is hard, preferably the waterwill be softened by lime softening, lime-soda ash softening orexcess—lime treatment.

Furthermore, the hydrated alumina may be used for the treatment of thesupernatant of the backwash water in the preparation of municipal water,thus ensuring that biological species such as Cryptosporidium isremoved. Backwash water is generated in water treatment plants byreversing the water flow through a filter in order to remove thematerial trapped. The backwash water is normally decanted and thesupernatant may be recycled to the head of works.

In a domestic water situation, the water will have already have beentreated by the normal processes as described above. However it is alwayspossible that viable micro-organisms may remain in the water supply ormay be introduced between the water treatment plant and the domesticuser. This may occur by for instance sewage infiltration to thereticulation system.

Whilst swimming pool water is not classified as potable water it isimportant that its microorganism contents is kept within standardlimits. This is particularly important in the case of public swimmingpools and spas. In order to maintain water quality swimming pool wateris desirably subjected to filtration and disinfection. As chlorine isinefficient as a disinfectant against Cryptosporidium it is important tobe able to remove it from the swimming pool water as the water is beingfiltered prior to recirculation.

An advantage of the present invention is that it may be readily utilisedas an adjunct to existing water treatment facilities. As mentionedabove, in most applications, the hydrated alumina bed will be used as afinal polishing filter. This permits an existing water treatmentfacility to be upgraded by retrofitting an additional stage after thecurrent water treatment stages.

The aluminium based medium, preferably hydrated alumina, may be packedinto a suitable, high flow rate filtration cartridge and may, forexample, be used as the final stage in a swimming poolpumping-filtration unit. Alternatively, such cartridges may be useddirectly in conjunction with a domestic water reticulation system. Inthis form, the cartridge may be fitted to tap(s) from which drinkingwater is to be obtained or to the inflow from the municipal watersupply.

In a domestic situation, it may also be appropriate to use a bed ofhydrated alumina contained within a gravity fed cartridge. In thissituation, water is simply fed under gravity through a cartridge that isopen to receive the water at one end and at the other end, allows thewater to drain into a receiving vessel. Alternatively, the hydratedalumina may be contained in a water permeable bag. In this situation,the bag containing the hydrated alumina is immersed in a vessel of waterto be treated for a suitable contact period.

For the majority of applications, the contact time between the aluminiumbased medium and the water to be treated will be minimal. Typicallycontact times of between about 5 seconds and 1 hour will be sufficientto achieve normal removal. The contact time is, however, dependent on avariety of factors applicable to each use situation such as the extentof the contamination, the available surface area of alumina for contactwith the water, i.e. particle size and volume of alumina, the surfacedensity of hydroxyl groups and the flow rate of water over or throughthe alumina. The person skilled in the art will appreciate that asuitable contact time may be established through appropriate testing andevaluation.

The surface density of Al—OH groups on the surface of the aluminiumbased media occurs ideally at an average rate greater than about 1hydroxy group per 10 nm² of surface (1 hydroxy group per 10 nm²),preferably greater than about 1 hydroxy per group 5 nm², 1 hydroxy pergroup 3 nm² especially 1 hydroxy per group 2 nm². Most preferably, thedensity of the surface hydroxy groups occurs at an average rate greaterthan about 1 hydroxy per group 1 nm², especially greater than about 1hydroxy per group 0.75 nm² or about 1 hydroxy per group 0.5 nm². Whenthe Al₂O₃ surface is essentially fully hydrated, thereby providing amaximized surface area available for adsorption of the biologicalspecies to be separated, the average rate of surface Al—OH groups pernm² of surface area, is about 1 hydroxy per group 0.18 nm² to about 1hydroxy per group 0.25 nm². In general terms, fully hydrated alumina ismost effective for the removal of biological species.

Because of the nature of the alumina surface, activated alumina(dehydrated alumina) still contains some hydroxylated sites for exampleless than about 1 hydroxy group per 10 nm². However, this material isineffective in removal of Cryptosporidium from contaminated water. Theintroduction of surface Al—OH groups onto activated alumina isthermodynamically favoured and can be achieved by hydrating methodsknown to those skilled in the art, for example activated alumina may besoaked with water for a prolonged time. A second method involvestreatment with sodium hydroxide (NaOH), where the upper alumina surfaceis dissolved thus allowing other hydroxyl groups to be formed. In athird method, the activated alumina may be treated by exposure toultraviolet light in the presence of water vapour. This process producesozone which breaks the Al—O—Al bond allowing the formation of Al—OH. Ina fourth method activated alumina is treated with, the peroxide producesa hydroxyl radical which attacks the Al—O—Al bond allowing the formationof Al—OH. These methods may be controlled to introduce the desiredfrequency of Al—OH groups over the surface area. By way of example, onlythe alumina surface may be hydroxylated by treatment of the alumina in1×10⁻²M NaOH or in 30% w/v/H₂O₂ for more than one hour or treatment withozone in the presence of water vapour.

In general terms, operation of the invention will result in at least a 1log reduction in the biological species present in the water. In thecontext of this specification, a log reduction refers to a 10 foldreduction. For example, if there were 1000 microorganisms per ml in awater sample, a 1 log reduction would result in 100 microorganismsremaining. A 2 log reduction would result in 10 microorganismsremaining. Preferably there will be a 2 log reduction, desirably a 3 logreduction, most preferably a 4 log reduction. It is especially preferredthat the invention operates to such that there is at least a 5 logreduction, particularly a 6 log reduction. Removal of the proportion ofthe biological species may be achieved in one treatment or, optionallythe process of contacting the contaminated water with the Al—OH surfacemay be repeated to provide the desired level of removal of thebiological species from the water.

As the following Examples describe, Cryptosporidium oocysts are found tostrongly adsorb onto alumina surfaces containing surface Al—OH groups.The results indicate that once adsorption onto the alumina takes place,the oocysts are strongly resistant to desorption, even in solutions athigher pH values, where the surfaces will be more negatively charged.Such an independence of pH is a process safeguard because the oocystswill not be released on the water due to small pH variations.

It appears that alumina is a specific substrate for Cryptosporidiumoocyst adsorption. The adsorbed oocyst layer appears to be stable andresistant to desorption with pH and EDTA treatment. Without limiting theinvention by theory, Cryptosporidium adsorption may be due to a specificchemisorption between the alumina surface and either the carboxylate orphosphate groups or some other groups present on the oocyst surface.

MODES FOR CARRYING OUT THE INVENTION

The invention will now be described with reference to the followingnon-limiting Examples and Figures. In these examples, removal ofCryptosporidium from water is described. It will of course beappreciated by persons skilled in the art that other biological species,particularly microbiological pathogens may be removed from water usingthis invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 depicts an electron micrograph of a Cryptosporidium oocyst.

FIG. 2 is a graphical representation of the change in zeta potential ofCryptosporidium oocysts in 10⁻³M NaCl as a function of pH.

FIG. 3 is a photograph of Cryptosporidium oocysts adsorbed onto polishedalumina wafers.

FIG. 4 schematically depicts a size comparison between Cryptosporidiumoocysts and individual alumina or silica spheres.

FIG. 5 schematically depicts the retention of Cryptosporidium oocystsonto packed and unpacked columns of silica and alumina.

FIG. 6 is a photograph of the optically smooth surface of an aluminawafer having a few extraneous dust particles.

FIG. 7 graphically depicts the permeate levels of Cryptosporidiumoocysts adsorbed after repeated washings through a silica column.

FIG. 8 graphically depicts the permeate levels of Cryptosporidiumoocysts adsorbed after repeated washings through an alumina column.

EXAMPLES Materials and Methods

The γ irradiated bovine Cryptosporidium oocyst samples were supplied byAustralian Water Technologies (AWT) at a concentration of 5×10⁶ and3×10⁸ oocysts/ml in distilled water which was stored at 4° C. prior touse.

The water used in this study was produced from tap water, which was fedthrough a Memtec Krystal Kleen™ unit using a three-stage purificationprocess (prefilter, reverse osmosis and activated charcoal) before beingdistilled, collected and stored in a positive pressure, dust freelaminar flow cabinet to prevent air borne contamination.

Pure alumina (α-Al₂O₃) in the form of flat, optically smooth 4 inchdiscs, was obtained from Silica Source Technology, Temple, Ariz., USA.

Alumina powder (63-200 μm diameter) was obtained from Merck (art. 1077).The alumina sample was fractionated in water to separate out only thelargest of the particles for column separation investigations. Thepurpose of selecting the largest particles was to prepare a packedcolumn of alumina in which the pores between the individual sphereswould be large compared with the size of Cryptosporidium oocyst (seeFIG. 4). Therefore any Cryptosporidium retention would be solely due toadsorption rather than a physical retention based on a size exclusionalone. The alumina was dispersed in aqueous solution, shaken and quicklyallowed to settle, the fine dispersed phase was decanted off and theremaining material redispersed. This process was repeated 20×, each timediscarding the dispersed material until only the largest particles wereretained.

In order to mimic conventional sand filter, parallel column filtrationexperiments were carried out using ballotini (glass) spheres ofdiameters greater than around 150 μm which were prepared in a similarfashion to the alumina particles. This enabled the preparation ofcolumns with sufficiently large pores that would prevent oocysts captureby size exclusion (see FIG. 4).

Adsorption Studies

Alumina substrates, immediately after cleaning using UV irradiation,were directly exposed to 100 μl of a 5×10⁶ oocysts/ml Cryptosporidiumsolution. The treated substrates were placed into a covered petrie dishhoused inside another larger moist petrie dish in a refrigerator forseveral hours allowing oocysts to adsorb to the surface. After this timethe liquid was decanted off and the substrate was rinsed with distilledwater. Any residual liquid removed by way of capillary action usingfilter paper. The substrate were then examined under a Kombistereo WildM32 light microscope having a magnification range 162-1000× using aIntralux 5000 optical fibre light source. The adsorption density wasphotographed with a Kodak 400 flexi clear film at a film speed of 200ASA using a Nikon camera.

Column Separations

(1) A slurry of the larges alumina particles (prepared as describedabove) was transferred to a glass chromatography column (28 mm O.D)containing a #3 glass sinter the excess liquid was run from the columnleaving a packed column having a depth of 5 mm (see FIG. 5). A 100 μl ofthe Cryptosporidium sample at 3×10⁸ oocysts/ml was diluted to 25 mls ina volumetric flask, 10 ml of this solution was then transferred to thealumina packed column, and the solution allowed to stand 15 minutesbefore being allowed to percolate through the alumina at a rate (10ml/hr) into glass vials. After the entire contents had come through, thecolumn was washed twice times with 10 ml of distilled water allowing itto percolate through at a similar rate to that of the originalCryptosporidium sample. Each 10 ml fraction was collected, transferredto a microelectrophoresis cell and examined using dark fieldillumination. This determination of the density and charge of anyparticles present.

(2) A slurry of the largest Ballotini spheres was transferred to a glasschromatography column (28 mm O.D) containing a #3 glass sinter theexcess liquid was run from the column leaving a packed column having adepth of 5 mm (see FIG. 5). A 100 μl of the Cryptosporidium sample at3×10⁸ oocysts/ml was diluted to 25 mls in a volumetric flask, 10 ml ofthis solution was then transferred to the packed silica column, and thesolution allowed to stand 15 minutes before being allowed to percolatethrough the silica at a rate (10 ml/hr) into glass vials. After theentire contents had come through, the column was washed three times with10 ml of distilled water allowing it to percolate through at a similarrate to that of the original Cryptosporidium sample. Each 10 ml fractionwas collected, transferred to a microelectrophoresis cell and examinedusing dark field illumination. This allowed determination of the densityand charge of any particles present.

Example 1 Direct Adsorption on Alumina

The Cryptosporidium oocyst sample received from AWT was 5×10⁶oocysts/ml. Since the oocysts are approximately 5 μm in diameter, thearea per oocyst of 1.9×10⁻⁷ cm² means the number of oocysts required tocover a 1 cm² substrate is 5×10⁶. In these studies we have used 0.1 mlsamples of the original 5×10⁶ oocysts/ml sample.

Pure alumina (α-Al₂O₃) wafers were cut to an appropriate size and UVirradiated at (λ185 and 254 mm) for 1 hr in the presence of water vapourto remove any organic contamination. The UV irradiation in the presenceof water vapour and oxygen produces ozone and hydroxyl radicals whichclean the alumina surfaces rendering them hydrophilic. After UVirradiation a small droplet of distilled water was placed on thesubstrates to ensure the surfaces were hydrophilic, then blown dry undera gentle stream of nitrogen.

The blank substrates were examined under a Kombistereo Wild M32 lightmicroscope having a magnification range 162-1000×. The alumina wafer washighly polished and so only dust contamination and the roughness of thereverse side of the wafer enabled us to focus on the smooth surface.FIG. 6 is a photograph of the microscope focussed on the opticallysmooth surface having a few extraneous dust particles attached. Thisindicated that the wafer would provide an excellent, optically smoothsurface for adsorption investigations using light microscopy.

The hydrated alumina wafer was directly exposed to 0.1 ml of a 5×10⁶oocysts/ml solution. The treated substrate was placed into a coveredpetrie dish housed inside another larger moist petrie dish in arefrigerator for several hours allowing oocysts to adsorb to thepositively charged surface. After this time the liquid was decanted offthe substrate and any residual liquid removed by way of capillary actionusing a filter paper. The substrate was examined in a similar manner tothat of the blank. When focussed on the alumina surface, a uniform layerof about 1/10th monolayer coverage of oocysts was observed (see FIG. 3)which is consistent with the original oocyst density (i.e. 5×10⁵oocysts), suggesting that all or most of the oocysts were recovered fromsolution by direct adsorption to the alumina substrate.

To test whether adsorbed oocysts could be easily desorbed, the coatedalumina substrate was placed into a covered beaker containing distilledwater for approximately 20 hours. After this time, the substrate wastaken out with the aid of tweezers and any residual liquid removed viacapillary action using a filter paper, it was then examined under themicroscope. The adsorption density of oocysts was unchanged, indicatingthat the adsorbed oocysts were stable in water at pH 5.7. This result isconsistent with the observation that alumina is positively charged atthis pH. Furthermore, it also indicates that Cryptosporidium oocystshave a high affinity for the alumina surface.

To test whether the oocysts would remain adsorbed to alumina substratesat higher pH values, the coated alumina was placed into buffer pH 9.2.At this pH the alumina becomes negatively charged which might causeoocyst desorption if the adsorption was purely electrostatic in origin.

However, after leaving the coated substrate for 16 hours at this pH thesubstrate was examined under the microscope, again no oocyst desorptionwas found to occur. This could be either because at this pH the(negative) surface potential is still too weak to overcome the strongvan der Waals attraction or because once the oocysts have adsorbed,strong short range ligand bonds are formed between the surface aluminiumand the carboxylate or phosphate groups present on the oocyst surface.To test whether the low surface potential could be the reason for thefailure to desorb, we placed the coated substrate in a pH 10 buffer(where the alumina should acquire a high negative surface potential) forseveral hours, again no oocyst desorption was observed. This providesfurther evidence that the resultant oocyst adsorption was due to arelatively strong specific chemisorption.

Example 2 Column Separators

A glass chromatography column (28 mm O.D) containing a #3 glass sinterwas chosen for column separations (see FIG. 5). In order to ensure thepores of the glass sinter were large enough to allow the Cryptosporidiumoocysts through, a 10 ml sample of 1.5×10⁶ oocysts/ml was passed throughthe glass sinter of the unpacked column.

The column permeate was collected and transferred to amicroelectrophoresis cell and examined using dark field illumination. Atthe first stationary level about 125 negatively charged particles(oocysts) were observed. This demonstrated that oocysts could easilypass through the glass sinter.

(2.2) Silica Blank

The silica Ballotini) spheres were fractionated to a size approx 200 μmin diameter as described earlier. The glass column was packed to a depthof 5 mm with the fractionated large Ballotini spheres. 10 ml ofdistilled water was allowed to percolate through the packed column andthe permeate collected. The permeate was transferred to amicroelectrophoresis cell. This not only allowed us to test whether thesinter was of sufficient porosity to retain the silica support but italso allowed determination of the background levels. The sinter wasfound to adequately retain the packing support since the permeatetypically had about 8 negatively charged particles in the field of view.

(2.3) Silica Packed Column

The silica (Ballotini) spheres were fractionated to a size approximately200 μm in diameter. A slurry of these spheres was transferred to a glasschromatography column (25 mm O.D) containing a #3 glass sinter theexcess liquid was run from the column leaving a packed column having adepth of 5 mm. A 100 μl of the Cryptosporidium at 3×10⁸ oocysts/ml wasdiluted to 25 mls in a volumetric flask, 10 ml of this solution was thentransferred to the packed silica column, and the solution allowed tostand 15 mins before being allowed to percolate through the silica at arate (10 ml/hr) into glass vials. After the entire contents had comethrough, the column was washed three times with 10 ml of distilled waterallowing it to percolate through at a similar rate to that of theoriginal Cryptosporidium sample. Each 10 ml fraction was collected,transferred to a microelectrophoresis cell and examined using dark fieldillumination.

The Cryptosporidium sample before passing through the packed supportcontained about 75-78 negatively charged particles at a given plane ofview within the cell. The permeate which was passed through the packedcolumn was seen to have about 70 negatively charged particles. Threefurther 10 ml washings were put through the column to see whether theCryptosporidium would desorb or whether there was a lag time involved intotal “Cryptosporidium” recovery. The first, second and third washingswere found to contain 34, 13 and 8 negatively charged particles,respectively. The results obtained are shown graphically in FIG. 7. Thisdemonstrates that Cryptosporidium was not retained in the column support(i.e. no adsorption evident) thus allowing the oocysts to travel throughlarge intra-pore spacing between adjacent silica particles.

(2.4) Alumina Blank

The alumina powder was fractionated to a size approximately 200 μm indiameter as described in materials and methods. The glass column waspacked to a depth of 5 mm with the fractionated alumina powder. 10 ml ofdistilled water was allowed to percolate through the packed column andthe permeate collected. The permeate was transferred tomicroelectrophoresis cell and set at the first stationary level. Thisallowed determination of whether the sinter was of sufficient porosityto retain the alumina support as well as background levels. The sinterwas found to adequately retain the packing support, since the permeatetypically had about 14 negatively charged particles at any plane ofview.

(2.5) Alumina Packed Column

The alumina powder was fractionated to a size approximately 200 μm indiameter as previously described. A slurry of this hydrated aluminapowder was transferred to a glass chromatography column (28 mm O.D)containing a #3 glass sinter. The excess liquid was run from the columnleaving a packed column having a depth of 5 mm. A 100 μl of theCryptosporidium at 3×10⁸ oocysts/ml was diluted to 25 mls in avolumetric flask, 10 ml of this solution was then transferred to thealumina packed column, and the solution allowed to stand 15 mins beforebeing allowed to percolate through the alumina at a rate (10 ml/hr) intoglass vials. After the entire contents had come through, the column waswashed twice with 10 ml of distilled water allowing it to percolatethrough at a similar rate to that of the original Cryptosporidiumsample. Each 10 ml fraction was collected, transferred to amicroelectrophoresis cell and examined using dark field illumination.This permitted determination of the density and charge of any particlespresent.

The Cryptosporidium sample before passing through the packed supportcontained about 70 negatively charged particles at a given plane withinthe cell. By comparison, the permeate which was passed through thepacked column was seen to have only 4 negatively charged particles (i.ebelow background level) at the given plane. Two further 10 ml washingswere put through the column to see whether the Cryptosporidium could beeasily desorbed. The second and third washings were found to containonly 1 negatively charged particle (see FIG. 8).

This demonstrated that Cryptosporidium was retained in the column due toadsorption, as the intra-pore spacing between adjacent alumina particleswould have presented no barrier based on size exclusion alone. Also,repeated washings provided good evidence that the oocysts could not beeasily desorbed.

Example 3

To investigate the various rapid rehydroxylation methods the alumina washeated to 610° C. and the powder treated either with H₂O₂ or NaOH. Thepowder was then dried in the oven at 110° C. to remove surface water andtested to see whether the powder fines floated or sank. The methoddeveloped involved taking a sample of the powder on the end of a spatulaand then as approach the surfaces at an angle of 45° the powder wasslowly moved through the air/water interface, the spatula was thenslowly withdrawn and if the powder was not fully hydroxylated thepowdered fines floated, whereas if the powder was fully hydroxylated inappeared to be wetted and ran off the end of the spatula.

NaOH Treated Alumina.

We tested the powders treated with 1×10⁻⁵, 5×10⁻⁴ and 1×10⁻²M NaOH foran hour. The powders treated with 1×10⁻⁵, 5×10⁻⁴ floated whereas the1×10⁻² M NaOH treated sample sank indicating that the particles ofalumina had become hydrophilic.

H₂O₂ Treated Alumina.

We tested the powders treated with 10% w/v H₂O₂ for ½ Hr and 1 hr andwith 30% w/v H₂O₂ for 5, 10, 15, 30, 60, 120 and 225 mins. We found thatthe powders<1 hr floated whereas times greater than 1 hr sank indicatingthat these experiments demonstrate that hydroxylation of alumina may beaccomplished in a rapid and efficient manner using treatment with eithersodium hydroxide of hydrogen peroxide solutions.

Throughout this specification and the claims which follow, unless thecontext requires otherwise, the word “comprise”, and variations such as“comprises” and “comprising”, will be understood to imply the inclusionof a stated integer or step or group of integers or steps but not theexclusion of any other integer or step or group of integers or steps.

Those skilled in the art will appreciate that the invention describedherein is susceptible to variations and modifications other than thosespecifically described. It is to be understood that the inventionincludes all such variations and modifications. The invention alsoincludes all of the steps, features, compositions and compounds referredto or indicated in this specification, individually or collectively, andany and all combinations of any two or more of said steps or features.

1-26. (canceled)
 27. A method for the removal of Cryptosporidium fromwater comprising the steps of contacting the water with a mediumcomprising particulate alumina having surface Al—OH groups occurring atan average rate of 1 hydroxyl group per 0.25 nm to 1 hydroxyl group per0.18 nm² for a time from 5 seconds to 1 hour so as to effect at least a1 log reduction of Cryptosporidium present in the water by adsorptionthereof onto said alumina.
 28. The method according to claim 27, whereinthe water has been pre-treated prior to contact with the medium.
 29. Themethod according to claim 27, wherein the medium is contained indiscrete filter beds, each filter bed comprising particles of alumina indifferent size ranges.
 30. The method according to claim 27, wherein themedium is contained in a cartridge.
 31. The method according to claim28, wherein the medium contained in a filter bed is used as a polishingfilter.
 32. The method according to claim 27, wherein the medium iscontained in a water permeable bag which is immersed in water to effectreduction of Cryptosporidium.
 33. The method according to claim 30,wherein the water is brought into contact with the medium under gravityflow.
 34. The method according to claim 27, comprising alumina having aparticle size of about 0.5 mm to 1.5 mm.